Remote control system



Feb, 17, 1942. c. s. SNAVELY ETAL 2,273,333

REMOTE CONTROL SYSTEM Fil ed Aug. 5, 1958 5 Sheets-Sheet l INVENTORS Clarence 5. Snauelg 6 Feb. 1942. c. $.SNAVELY ET AL 2,273,383

REMOTE CONTROL SYSTEM Filed Aug. 5, 1938 5 Sheets-Sheet 4 P8 P9 P10 P11 P12 P1 P2 P5 P4 P5 P6 P7 b b b 1 9 P9 P10 P11 p STATION P7 P2 P5 P4 R: P6

P8 P9 P10 P11 INVENTORS C'lamnee56m0elg 6? BY fmdRMflep.

a 1i mm A'l'ro'RNEY Feb. 17, 1942.

c. s. SNAVELY ET AL 7 REMOTE CONTROL SYSTEM Fi led Aug. 5, 1958 s Sheeis-Sheet 5 do nd m Y mm. m m lmwg eA am Wmqm d T Patented Feb. 17, 1942 UNITED STATES PATENT OFFICE REMOTE CONTROL SYSTEM Application August 5, 1938, Serial No. 223,287

25 Claims.

.Our invention relates to remote control systems for the control from a central point of selected devices located at remote points, and for also indicating at the control point the condition of such devices and other devices at remote points. In its'specific embodiment, our invention relates to centralized trafiic control systems lfor railroads of the type in which a large number of railway signals and track switches at different stations along the track are controlled ,from time to time from a dispatchers office over a single line circuit, and in which the same line circuit is also employed at other times to indicate .the positions assumed by the switches and signals and also to indicate the presence of trains at the same or at other field stations.

Our invention comprises a code signalling system employing a single line circuit normally energized by current of a given relative polarity in which the line is first opened and then a code of short and long impulses of the reverse polarity is transmitted so that in a series of codes the code impulses are all of the reverse polarity but the codes are spaced definitely by impulses of normal polarity.

One object of our invention relates to the provision of a relatively simple and reliable code signalling system in which all the operations of generating and receiving codes are performed by relays, and which functions in such a manner that the control oflice may be located at either endor at an intermediate point in the line circuit and the difierent control and indication codes will be transmitted one at a time in a predetermined order even though two stations or theofiice and a station start to transmit at the same time. In respect to the means by which this object is attained, our invention is ,an improvement over those disclosedin the copending applications, Serial No. 31,592, filed July 16, 1935, by =Snavely, Miller and Jacltel, now Patent No. 2,183,155,.granted December 12, 1939, and Serial No. 222,860, filed AugustB, 1938, by Snavely and Miller,,for Remote control systems.

The invention of the present application relates particularly to a communication system providing two-way communication over a line circuit in which the initiation of a multiple element impulse code establishes a given direction of transmission in accordance with the character of its first element, and in which the codes are normally delivered to the line circuit in the order in which they are initiated, successive codes being spaced by time intervals during which the line'is idle. An object of our invention is the provision of means for storing codes for subse quent transmission as long as the line is in use, and for maintaining an established direction of transmission as long as there are codes stored for transmission -in that direction, the stored codes being transmitted in a group, in a given order of code superiority. A direction determining code element is transmitted only in the first code of a group, and the successive codes of a group are spaced by relatively short time intervals so that the average speed of transmission is thereby materially increased.

Another feature of our invention resides in the provision of means for preventing the transmission of any code which becomes stored after the transmission of a group of codes has been rality of codes are initiated at the same time.

Other objects and features of our invention will become apparent as thedescription proceeds.

We shall describe one form ofapparatus embodying our invention, and shall then point out the novel :features thereof in claims.

In the accompanying drawings, Figs. 1A, 1B,

2A, 2B and 3, inclusive, form a diagrammatic View illustrating in condensed form one arrangement of apparatus employed in a centralized traffic control system embodying our invention. More particularly, Figs. 1A and 1B, taken to,-

. gether, comprise thedispatchers ofiice equipment for generating and delivering codes to the line circuit for transmission to one station, and for receiving codes from that station and operating the appropriate indication devices of the corresponding ofilce panel. As hereinafter explained in detail, this apparatus may be readily expanded by duplicating certain portions so that it may be used to control and indicate apparatus at thirty-two different stations, corresponding to the maximum capacity of the system as herein illustrated, in which case the office equipment will include thirty-two individual panels each similar to the one shown at the right in Fig. 13. Figs. 2A and 2B, taken together, comprise the equipment at one field station. The equipment at all the stations is alike, the different stations being distinguished by an appropriate arrangement of jumper connections, so that each is adapted to send and receive a particular code call characteristic of the station, Fig. 3 illustrates a typical arrangement of apparatus controlled by the apparatus of Figs. 2A and 2B for directly controlling the railway signals and track switches at a station and for initiating and determining the character of the indication codes.

Similar reference characters refer to similar parts in the several views.

Before proceeding with a detailed description of the circuits, we shall briefly explain the general plan and organization of our apparatus.

In the specific embodiment of our invention herein illustrated, each control code consists of a series of twelve impulses, while each indication code has fourteen impulses. The first step of a code initiated while the line is free is employed to select the direction of transmission. The first step of a control code initiated when the line is free is a short negative impulse, while the first step of an indication code initiated when the line is free is a long negative impulse. When the direction of transmission is once established. it is maintained as long as there are codes stored for transmission in the same direction, and in each of the succeeding codes of a series the first step is a short positive impulse, irrespective of whether these are control codes or indication codes. All of the remaining steps of each code are negative except the last step, which comprises a short positive impulse.

The five impulses immediately following the first impulse may be arranged to provide thirtytwo difierent combinations of short and long impulses for station selection in case of control codes, or for the selection of the office panel corresponding to the transmitting station in the case of indication codes. The remaining impulses are described as function elements, and in the case of a control code the lengths of the seventh, eighth, ninth and tenth impulses are determined each in accordance with the position of a diiferent control lever of the corresponding panel. The seventh step is controlled by the switch lever SW, Fig. 1B; the eighth and ninth steps by the signal levers LG and RG, respectively; while the tenth step is controlled by an auxiliary or callon signal lever CO. Each of these steps is short when the lever is in the position shown and long when the lever is reversed, and at the selected station each of these impulses is stored,

and when the next succeeding impulse is received a polar stick relay W S, LHS, RHS, or CHS, Fig. 2B, is operated to a position corresponding to that of the associated lever. That is, these relays are operated during the eighth, ninth,

tenth and eleventh steps of the code, and they control the track switch and railway signals of Fig. 3 in a manner hereinafter pointed out.

The seventh and eighth steps of an indication code are controlled by a switch indication relay KR, and are both short when the track switch is locked normal; the seventh is long and the eighth short when the switch is locked reverse; and the seventh is short and the eighth long when the switch is unlocked or when relay KR. and the associated switch control relay WS are not in corresponding positions. At the oifice, the indication relays IWK and ILK governing the switch indication lamps NWE and RWE are operated in accordance with the character of the seventh and eighth steps during the eighth and ninth steps, respectively, lamp NWE or RWE being lighted when the track switch is locked in the corresponding normal or reverse position in agreement with the position of the switch control relay WS.

The ninth and tenth steps of an indication code are controlled by two signal indication relays LGP and RGP, respectively, so that both these steps are short when the signals LG and RG are at stop, and the ninth or tenth step is long when the corresponding signal is clear. At the office, these steps control the polar stick signal indication relays ILGK and IRGK during the tenth and eleventh steps, respectively. The signal indication relays cause a lamp NGE to be lighted to display a stop indication when the ninth and tenth steps are short, or cause the corresponding lamp LGE or RGE to be lighted to display a clear signal indication when the corresponding step is long.

The eleventh and twelfth steps are controlled respectively by the track relay ITR for the switch section t, Fig. 3, and by an approach relay lAR, which releases when a train occupies the approach zone comprising sections u and 12. These relays when released cause the transmission of long impulses to reverse the respective indication relays ITK and IAK during the twelfth and thirteenth steps, respectively, thereby causing lamp ITE or IAE to indicate that the corresponding track section is occupied.

The apparatus at the office and stations is generally similar and with a few exceptions, which will be pointed out as the description proceeds, corresponding relays at the oflice and stations operate in unison on each step. Each code is initiated by releasing a normally energized starting relay such as relay Si, Fig. 1B, or relay S, Fig. 2B, which when released stores the code for transmission, and when the line becomes available operates the corresponding code sending relay SP to start transmission.

The line circuit, identified on the drawings by the reference 5, includes in series a positively biased polar line relay LI, a negatively biased polar line relay L2, and back contacts a and b of a transmitter relay T or OT at the office and at each station, and at the office, as shown in Fig. 1A, also includes a line battery, identified by the terminals LB and LC, respectively, which is connected to the line through the winding of an auxiliary relay LO, key K2, and contacts a and b of a pole changer relay PC.

It will be understood that the portion of line 5 shown in Fig. 1A, and a plurality of portions of line 5, one for each station, each similar to the portion shown in Fig. 2A, are connected by line wires to form a single closed circuit which is normally energized by current supplied by the ofiice line battery. This current is normally of the proper polarity to cause the relays L! to be picked up, while the relays L2 which operate on current of the opposite polarity normally occupy their released positions, as shown. During code transmission, the polarity is reversed so that each relay Ll remains released and the relays L2 are operated in unison in accordance with the code generated by the repeated opening and closing of the line circuit by relay OT, in c ase of a control code, or by one of the relays I, in case of an indication code.

The pole-changer PC is restored to its normal position during the line-open interval preceding the last impulse, which therefore is positive and operates the line relays Ll, relays L2 remaining released. Relays Ll are again energized and pick up when the line is restored to normal at the end of a code.

Each line relay L2 controls a group of intermediate stepping relays X2, Y2, X8 and Y3 which are operated repeatedly one at a time in that order as relay L2 alternately picks up and releases, to count the steps of the code, and also controls two groups of cascade-connected timing relays A2, B2, C2, D2, and A3, B3, C3, D3, which are operated alternately in series with difierent ones of the stepping relays, and serve to measure and register the short or long character of the successive steps, and to operate a main series of stepping relays Pl to PIS, inclusive;

On each station selecting step the corresponding relay P is operated only if the stepis a particular character, the successive operation of a particular series of relays P2 to P6, inclusive, constituting the station or panel selection. On the function steps, relays P prepare circuits for th polar stick control or indication relays successively so that each such relay will be positioned on a different step in accordance with the relative length of the next preceding step. Each relay P is operated during the line-open period which precedes the correspondingly numbered impulse of the code.

Each line relay Ll controls a group of similar stepping relays X0, Y0 or XI in series with the timing relays A0 or the relays Al, Bl, Cl, the

operation of which governs the restoration of the apparatus to normal at the end of a code.

At the transmitting station, after relay T or OT has been initially energized by the operation of relay SP to open line 5 it is released by relay PI and is then placed under the control of the remaining relays P by the operation of a master relay M or OM which is energized in accordance with the character of the first step. Each relay P prepares a different circuit for relay T or OT which is so controlled by the intermediate stepping and timing relays as to give the desired character to the next impulse, the action being such that when once initiated relay T or OT is operated repeatedly by the P relays which it controls until the code is completed.

A number of the relays employed in our apparatus are rendered slow release by the connection of asymmetric units of the copper oxide rectifier type in multiple with the relays, as shown conventionally for relay AO, Fig. 1A, for example. These units present a high resistance to the flow of current from the power source while providing a low resistanc discharge path to permit the gradual discharge of the stored inductive energy of the relay when the power source becomes disconnected. The stepping relays X, Y and P are in this manner arranged to have sufficient retardation to hold them picked up in each case until other relays have picked up, while the timing relays A, B, C, D, etc. are arranged to have a definite constant time period so chosen as to provide the proper rate or operation and to so measure the relative lengths of the different impulses as to insure a wide margin against incorrect operation.

While any suitable relays may be used, the code relays shown herein are preferably of the types shown in the Snavely applications Serial No. 139,535, filed April 28, 1937, now Patent No.

2,140,604, granted December 20, 1938, and Serial No. 141,311, filed May '7, 1937, now Patent No. 2,178,289, grantedOctober 31, 1939, for Electrical relays.

Referring now to Fig. 3, the track diagram at the top represents a stretch of railway track including a track switch to and a group of signals LA, LB, LC, RA, RB and RC for governing traffic movements over the switch, corresponding to one end of a passing siding on a single track railway. The circuits of Fig. 3 represent one arrangement of interlocked switch and signal control apparatus which the polar stick relays WS, LHS, RHS and CH5 of our station equipment as shown in Figs. 2A and 2B are adapted to control. As indicated conventionally in Fig. 3, the code-responsive switch control relay WS of Fig. 2B controls the switch machine SM so as to operate the track switch 21; to a position to correspond with' that of its contact a, and its contact 1) permits the energization of the switch indication relay KR in a direction corresponding to the position of switch w and relay WS. Contacts a, b and c of relay KR govern the transmission of switch indication codes as hereinafter described in connection with Figs. 2A and 2B.

The signals shown in Fig. 3 are assumed to be of the light signal type and each is controlled by a signal relay HR. When all the signals for one direction are at stop, the corresponding signal indication relay RGP or LGP is energized, which at its contacts a. and b governs the transmission of signal indication codes as hereinafter described, and at its contact 0 controls an approach locking stick relay LAS or RAS. The detailed circuits for relays LAS and RAS have been omitted, to simplify the drawings, but these may be arranged, for example, as shown for relays M5 and M6 of the Wallace Patent No. 1,959,- 972, granted May 15, 1934. The approach looking relays together with the track relay TR for th switch section 22 control a switch locking relay L which opens the circuitsfor switch machine SM when a signal has been cleared or the switch is approach locked.

Contacts a and b of the track relay TR and the approach relay AR govern the transmission of track indication codes by the apparatus of Figs. 2A and 2B, and the manner in which these relays are controlled to effect the transmission of indications of track conditions will be apparent from the drawings.

The main signal relays I-IR having the prefixes A and B for governing train movements over the main track and siding, respectively, are controlled in. accordance with the position of relay KR by the code-responsive signal control relays RHS and LHS. The circuit for relay RAHR, for example. which is typical, may be traced from one terminal B of a suitable local battery, contact a of relay LAS, normal contact a of relay LHS, reverse contact a of relay Rl-IS, neutral contact d anu normal polar contact e of relay KR, contact d of relay TR, contact a of a polarized line relay RHR, relay RAHR to the other terminal C of the local battery. The circuit for relay RBI-IR is generally similar, and it will be apparent that to clear signal RA or RB the operator will initiate a code to operate relay WS to normal or reverse as required and will then reverse relay RHS by code. or he may put signal RA or RB to stop manually by operating relay RHS to normal by code. Similarly, signal LA or LB may be cleared by the reversal of relay LHS by code.

It is to understood that relay RHR is controlled in accordance with traffic conditions at a. ,-cn and that signal RA is arranged in the usual manner to indicate clear, caution or stop in accordance with the conditions of relays RHR' and RAl-IR. Signals LA and LB are similarly controlled by conditions relating to the opposite direction, while signal RB governing traffic movements into the siding is a two-position signal.

The circuits for the slow speed signal relays RCHR and LCHR are arranged in the usual manner so that the signals which these relays control can be cleared only when traffic conditions are such as to prevent the clearing of the corresponding main signal. It will be apparent from the drawings that the clearing of signal RC or LC requires the call-on relay CHS to be reversed, by code, to close its contacts a and b in addition to the reversal of the corresponding signal control relay LHS or RHS.

The transmission of a typical contro1 code will now be described in detail. It will be assumed that the apparatus is in the condition shown in the drawings, and that the code is initiated by a movement of the switch lever SW, Fig. 1B, which controls the track switch at station No. 1, from normal to reverse, and that the corresponding station code call is represented by one long impulse followed by four short impulses.

The movement of lever SW at the office opens a normally closed starting circuit I which may be traced in Fig. 13 from one terminal B of a suitable local battery over contact a and the lower winding of the starting relay SI, contacts a of levers SW, LG, RG and C of panel N0. 1 to the other terminal C of the local battery. Relay SI releases whenever one of the levers is moved, and at its contact 9 completes a circuit 2 from terminal B at contact 0 of relay ST, Fig.

1A, contacts g of relays OM and SI, through the ergizing circuit 4 for the transmitter relay OT which extends from terminal B over contact b of relay SPI, the back contacts 9 of relays SRI, P6, P5, P4, P3, P2, PI, contact 6 of relay CI, contact g of relay BI, contact d of relay X0,

contact a of relay ST, relay OT, to terminal C.

Relay OT therefore picks up and at its contacts a and 1) opens the line circuit 5, releasing the plus line relays LI at the office and at all stations.

When each line relay LI releases, its contact 0 opens a normally closed circuit 6 which may be traced in Fig. 1A and also in Fig. 2A, from terminal B, contact 0 of relay LI, the upper winding of relay XI, contact a and the lower winding of relay YO, contacts 71. of relays AO, AI and BI, contact b and winding of relay CI to terminal C. At the same time, circuits I are closed from terminal B over back contact d of each line relay LI, contact 02 of relay L2, the upper winding of relay Y3, contact 17 of relay X3, contact e of relay CI, contact a and the lower winding of relay XI, contact 9 of relay AI, contact a and winding of relay CI to terminal C. It follows that relay Y3 picks up, relays XI and CI are held energized and relay YO releases at the office and at each station.

At the office the closing of back contact b of relay LI completes a circuit 8 fromv terminal B over contact 0 of relay XI, the right-hand winding of the pole changer relay PC to terminal C.

Relay PC therefore operates its contacts a and b to the right so that when relay OT releases the polarity of the current supplied to the line circuit 5 will be reversed.

When each relay YO releases, a pick-up circuit 9 is closed for the associated relay PI from terminal B, back contact d of relay YO, shown at the upper right in Figs. 1A and 2A, over contact c of relay Y3, contact d of relay CI, relay PI to terminal C. Relay YO at the ofiice also opens circuit II, releasing relay ST. When each relay PI picks up, it completes at its contact a a stick circuit III which is a branch of circuit 9 bridging contact d of relay CI When relay PI at the office picks up, its back contact 9 opens circuit 4 to release relay OT to terminate the first line-open period of the code.

First stepShort Since relay PC is now reversed, the closing of line 5 by relay OT causes the minus line relay L2 to pick up at the oflice and at each station, relays LI remaining released until the next to the last step of the code is completed.

Each relay L2 at its front contact a completes a circuit I2 from terminal B, the upper winding of relay X2, contact a and the lower winding of relay Y3, contact 0 of relay CI, relay A2 to terminal C, so that X2 and A2 pick up. At the same time, relay L2 opens circuit I to release relays XI and CI while relay Y3, being included also in circuit I2, is held energized.

It will be noted from Fig. 2A that circuit I2 at the station and also circuit 22 differ slightly from the corresponding ofiice circuits in that they extend to terminal B over contacts 0 and b, respectively, of a relay Z for a purpose hereinafter described.

When relay XI at the ofice releases a pickup circuit I3 for relay OT is closed which is the same as circuit 4 from terminal B to contact 9 of relay P2 and then extends over contact e of relay PI, contact 1 of relay A2, contacts d of relays X3 and XI, relay OT, to terminal C. Relay OT therefore picks up over circuit I3 to open line 5. The release of relay XI opens circuit 8, but relay PC is of the polar stick type and holds its contacts closed in the reverse position.

It will be noted that relay CI is deenergized at the same time as XI. Relay CI has a release period greater than that of XI, but if the period of any relay CI is less than normal so that it releases before the end of the step, circuit I2 will be opened at contact 0 of relay CI and a branch I4 of that circuit will be closed to maintain relays X2 and Y3 energized in series with relay B2. Circuit I4 may be traced from terminal B, contact a of relay L2, relays X2 and Y3, contacts a of relays CI, A3, C3 and D3, contact I) of relay A2, relay B2 to terminal C, so that relay B2 will pick up in series with relays X2 and Y3.

When line 5 opens the line relays L2 release and each closes a circuit I 5 from terminal B, back contact d of relay LI, back contact b of relay L2, through the upper winding of relay Y2, contact a and the lower winding of relay X2, contact a and the winding of relay A2 to terminal C, and at the same time relay L2 opens contact a in circuits I2 and I4. Therefore. re lay Y2 picks up, relays X2 and A2 are held energized, and relay Y3 releases. Relay B2, if picked up, becomes deenergized and releases.

When each relay Y3 releases, it completes a pick-up circuit I6 for relay P2 from terminal B over contact 01 of relay YO, contact c of relay Y2, contact 02 of relay Y3, contact I) of relay PI, relay P2, to terminal C, and at the same time, each relay Y3 at its contact '0 opens the stick circuit ill for relay PI so that PI releases. When each relay P2 picks up, it completes a stick circuit I'I extending to terminal B over its own contact a, contact of relay Y2, and contact d of relay YO.

When relay Y3 at the office releases, it closes at its back contact cl a circuit I3 for the oflice master relay OM from terminal B, back contact d of relay YO, Fig. 1A, contact 0 of relay Y2, contacts d of relays Y3, A2 and Pi, relay OM to terminal C. Relay OM picks up and completes its stick circuit I3 which extends to terminal B over contact a of relay OM, contact g of relay Cl and contact b of relay X0. Relays X0 and CI remain deenergized, and therefore relay OM remains picked up until the code transmission is completed.

W'hen relay Y3 at each field station releases, it closes at its back contact d a circuit I26 for the control code register relay CR from terminal B, contact at of relay YO, Fig. 2A, contact 0 of relay Y2, contacts d of relays Y3, A2, and PI, relay CR to terminal C. Relay CR picks up and completes a stick circuit I2! which extends to terminal B over its contact a and contact h of relay Cl. Relay CR remains energized until the code transmission is completed.

When the office relayP2 picks up it opens the energizing circuit I3 for relay OT at its back contact g, so that relay OT releases to close the line circuit 5.

S econd step-Long When each line relay L2 picks up, it closes a circuit 22 from terminal B over its contact 0, relays X3 and Y2, back contact 7' of relay AI, contact 0 of relay A2, relay A3 to terminal C. Each relay L2 at its contact 1) opens circuit I5. Relay X3 picks up and relays Y2 and A3 are held energized over circuit 22, while relays X2 and A2 release.

Relay A2, upon releasing, opens circuit 22 at its contact 0, deenergiaing relay A3, but maintaining relays Y2 and X3 energized and picking up relay B3 over a branch 23 of circuit 22 including back contacts 7' of relays A2, C2 and D2 and front contact b of relay A2. When relay A3 releases, its contact b opens circuit 23, deenergizing relay B3. Relays Y2 and X3 are now maintained energized and relay C3 picks up over a branch circuit 2 3 which includes back contact In of relay A3 and front contact b of relay C3.

When relay B3 releases, its contact 12 opens circuit 2 deenergizing relay C3. Relays Y2 and X3 are now held energized and relay D3 picks up over a branch circuit 23 which includes back contact h of relay B3 and front contact 19 of relay C3.

W'hen relay B3 at the office releases, a branch 260i circuit i for relay O-T becomes closed, which extends from terminal B over front contact e of relay P2, contact I of relay C3, contact g of relay B3, contact e of relay OM, contacts d of relays X2 and Xi, relay CT to terminal C. Relay OT new picks up to open line 3.

It is to be understood that the code sending relays SP for the oifice panels for the sixteen stations for which the second step, comprising the first element of the station call, is a long impulse, are arranged, as shown for relay SPI, to effect the energization of circuit 23. The code sending relays SP for the remaining sixteen stations, for which this step is a short step, are

arranged with a connection from their contacts I) to contact instead of to contact e of relay P2 to eiiect the energization of a branch circuit 21 on the second step. Circuit 21 extends from terminal B at contact b of the respective relay SP, not shown, over contact of relay P2, contact j of relay A3 and joins circuit 26 at contact e of relay OM. When circuit 21 has been prepared, it closes as soon as relay X2 releases at the beginning oi the second step. It will be apparent that the second step will be short when circuit 22 is used and will be long when circuit 26 is used.

At the end of the line-closed portion of the long second step, it will be found that relays Y2, X3 and D3 are energized and relay C3 deenergized. If relay C3 is still in its energized position, the release of each line relay L2 will close a circuit 28 at its contact d through relay Y3, contact a and winding of relay X3, contact g of relay A3, contact a and winding of relay C3, while if relay C3 has released, the branch 29 will be closed over contact 9 of relay 03, contact wand winding of relay D3. At the same time circuit 22 is opened at contact 0 of relay L2 so that relay Y2 will release. It follows that relay Y2 will release, Y3 will pick up, and X3 and C3 or D3 will be held energized.

When the oflice relay Y2 releases it closes the pick-up circuit 33 for relay P3 from terminal B over contact (1 of relay YO, contact 0 of relay Y3, contacts 01 of relays Y2 and C3 or D3, contact I) of relay P2, relay P3, to terminal C, and relay P3 picks up to close its stick circuit 33 comprising a branch of circuit Ill.

If the second step were short instead of long relay A3 would be held energized over a stick circuit comprising a branch 3| of circuit 28 in place of relay C3 or D3, and a branch circuit 32 would be closed when the ofiice relay Y2 releases, o-ver contact 0 of relay P2 to energize another relay corresponding to P3 but not shown.

It is to be understood that the ofiice relays P are connected in pyramid formation, and when the apparatus is arranged for the control of the full complement of thirty-two stations, it includes two relays like P3, each of which controls two relays like P4. Each of the latter controls two relays like P5, each of which in turn controls two relays like P3. Each of the PB relays controls a difierent series of relays P1 to PI3. That is, there are sixteen sets of relays like the relays P1 to PI3 of which but one set, namely the one associated with stations Nos. I and 2, is shown. It will be clear that only one series of relays P will be operated by any one code, but that any two codes which differ only in the character of the sixth element will operate the same series of P relays.

At each field station, when relay Y2 releases it closes a circuit I30 or I32 similar to circuit 3!) or 32. At sixteen of the stations circuit I30 is arranged as shown in Fig. 2B to include the station relay P3 and circuit I32 includes the winding of a lock-out relay Z, while at the remainder relay Z is included in circuit I 30 and relay P3 in circuit I32 by an interchange of jumper connections in a manner which will be apparent from the drawing. The circuit I32 for relay Z, as shown, extends from terminal B at contact at of relay YO, contact 0 of relay Y3, contacts 01 of relays Y2 and A3, contact 0 of relay P2, relay Z to terminal C. As shown, the

- station apparatus is arranged to receive a code in which the second step is long, in which case the station relay P3 picks up and by closing its contact a completes its stick circuit 33. If a code is received in which the second step is short relay Z picks up and is held energized over a stick circuit I33 extending to terminal B over its own contact a and contact b of relay XI until relay XI picks up at the end of the code. In either case relay Y2 opens circuit IT to release relay P2. As will be apparent from the drawing, similar circuits for relay Z are provided over contacts of relays P3, P4, P and P6. It follows that relay Z picks up on any station selecting step of a character to which the station apparatus is not intended to respond and by opening its contacts I) and c prevents further operation of the stepping apparatus at that station during that particular code.

When the office relay P3 picks up, it opens the energizing circuit or 21 for relay OT at its back contact 9 so that relay OT releases to close line 5.

Third step-Short When each line relay L2 picks up, it closes at contact a a branch 34, or 36 of circuit I2 to pick up relays X2 and A2 and to hold Y3 energized, the particular branch closed depending upon which of the relays C3, D3 or A3 are picked up at the time. These circuits differ from circuit I2 already traced in that they include a contact 0 of relay C3, D3 or A3, respectively, in place of contact 0 of relay CI. Relay L2 at its contact (1 opens circuit 28, 23, or 3|, deenergizing relay X3 and relay C3, D3 or A3, as the case may be.

When relay X3 at the ofiice releases, a pick-up circuit 31 for relay OT is closed which is the same as circuit 4 from terminal B to contact g of relay P4 and then extends over contact 6 of relay P3, contact 0 of relay OM, contact 1 of relay A2, contacts d of relays X3 and XI, relay CT, to terminal C. Relay OT picks up over circuit 31 to open line 5.

It is to be understood that the code sending relays SP for all stations for which the station call includes a short third impulse are arranged as shown for relay SPI to effect the energization of circuit 31 on the third step. The code sending relays for all stations for which this step is a long impulse are arranged to provide a connection from terminal B to contact of relay P3 to effect the energization of a branch 38 of circuit 4 which extends from contact b of the respective relay SP over contact I of relay P3, contact (1 of relay OM, contact f of relay C2, contact 9 r of relay B2, contacts cl of relays X3 and XI, relay OT, to terminal C.

In the event circuit 38 is prepared in place of circuit 37, the energization of relay OT is delayed until relays A2 and B2 release consecutively at the oilice and stations. One of the relays C3, D3 or A3, it will be remembered, becomes deenergized at the beginning of the third step, and upon releasing opens circuit 34, 35 or 36 at its contact 0, deenergizing relay A2, and at the same time by closing its contact 7' completes circuit I4 to pick up relay B2 in series with relays X2 and Y3. Relay A2 upon releasing opens circuit I4 at its contact 1), closing a branch circuit 39 at its contact h to pick up relay C2 in series with relays X2 and Y3 over front contact b of relay B2. Relay B2 upon releasing opens circuit 33, closing a branch circuit 43 at its contact h to pick up relay D2 in series with relays X2 and Y3 over front contact b of relay C2, and at the same time relay B2 at the oilice by closing contact g completes the above-mentioned circuit 38 for relay OT to terminate the long third step by opening line 5.

It follows that at the end of the line-closed portion of the third step, relays X2 and Y3 Will be energized in series With relay A2 if the step is short, and in series with relay C2 or D2 if the step is long. If the step is short, the release of each line relay L2 will close circuit I5, as on the first step, to pick up relay Y2 and to hold relays X2 and A2 energized, and at the same time circuit 34, 35 or 38 will be opened at contact a of relay L2 to release relay Y3.

The ofiice relay Y3 at its back contact d then completes a branch 4| of circuit I8 from terminal B at contact (1 of relay Y0 to pick up relay P4. At eight of the sixteen stations at which relay P3 is energized, the station relay P4 similarly picks up over a corresponding circuit I4I, While at the other eight stations of the group the jumper connections are interchanged so that relay Z picks up when circuit MI is energized. At all sixteen stations, relay Y3 opens circuit 33 to release the associated relay P3. Each energized relay P4 upon picking up completes a stick circuit 42 similar to circuit I! already traced.

If the third step of a code is long, relay C2 or D2 is picked up when relay L2 releases, and a branch 43 or 44 of circuit I5 is closed to pick up relay Y2 and to hold relays X2 and C2 or D2 energized, and relay Y3 upon releasing completes a pick-up circuit 45 and I45 for the corresponding relays P4, these circuits being similar to circuit 4| except that they include front contacts 11 of relays C2 and D2 in place of contact (1 of relay A2.

When the ofiice relay P4 picks up, it opens at its contact g circuit 37 or 38 to release relay OT to close line 5.

Fourth stepShort When each line relay L2 picks up, it closes circuit 22 to pick up X3 and A3 and to hold Y2 energized, and opens circuit I5, 43 or 44 to release X2 and A2, C2 or D2, as the case may be. When the ofiice relay X2 releases, a branch 46 of circuit 2'! is closed over contact e of relay P4 to pick up relay OT when relay X2 releases, to open line 5. In transmitting codes in which the fourth step is long, a branch 4! of circuit 26 is closed over contact I of relay P4 to pick up relay OT when relay B3 releases, to open line 5.

When each line relay L2 releases, it closes circuit 3| to pick up Y3 and to hold X3 and A3 energized, and opens circuit 22, releasing Y2. Relays Y2 at their back contacts d complete branches 48 and I48 of circuits 32 and I32 to pick up relay P5 at the ofiice and at four of the eight stations at which relay P4 is energized, relay Z picking up over circuit I48 at the remaining four of these stations. Relays Y3 at contacts c open circuits 42 to release all the energized relays P4. Each relay P5 that picks up completes its stick circuit 49. In the case of codes in which the fourth step is long the corresponding ofiice relay P5 is picked up over a branch 50 of circuit 30, while at the stations responsive to such codes relay P5 is picked up over a branch of circuit I30, as will be apparent from the drawing. The oflice relay P5 upon picking up opens its contact g in circuits 46 and 41 so that relay O'I' releases to close line 5.

Fifth sitep.5'hort When each line relay L2 picks up, it closes circuit36'to pick up relays X2 and A2 and to hold Y3 energized, and opens-circuit 3|, releasing relays X3 and A3. When the ofiice relay X3 releases a branch 5I of circuit 3'! is closed over contact e of relay P5 to pick up relay OT to open line 5. In transmitting codes in which the fifth step islong, a branch 52 of circuit 38 is closed at'this time over contact 1 of relay P5 to pick up relay OT when relay B2 releases, to open line 5.

When each line r-clay L2 releases, it closes circuit I5 to pick up Y2 and to hold X2 and A2 energized and opens circuit 36, releasing Y3. Relays Y3 at their back contacts 11 complete branches 53 and I53 of circuits 4| and I M, respectively, to pick up relays P6 at the oflice and at two of the four stations at which P5 is energized, relay Z picking up over circuit I53 at the other two stations of this group. Relays Y3 at their contacts open circuits 49 to release all energized relays P5. Relays P6 at the ofiice and at the two selected stations pick up and complete their stick circuits 54. In the case of codes in which the fifth step is long, the corresponding relays P are picked up over branches of circuits 45' and I45, such as the circuit 55 of Fig, 1B. The office relay P6, upon picking up, opens its contact g in circuits 51 and 52 so that relay OT releases to close line 5.

Sixth step-Short closed from terminal B at contact b of relay' SPI, contact g of relay SRI, contact cl of relay P6, the upper winding of relay SI, and thence over the same path as for circuit 21 through relay OT to terminal C. Relays SI and OT pick up in series, relay SI completing its normally closed stick circuit I at contact a, and relay OT opening line 5.

A code in which the sixth step is long is initiated' by the release of a different starting relay such as S2, in which case a circuit 51 is' closed from terminal B at contact bof relay SP2, contact g of relay SR2, contact 1 of relay P6, the upper winding of relay S2 and thence over the same path as for circuit 26 through relay CT to terminal C; circuit 51, when effective, being completed when relay B3 releases.

When line relay L2 releases it closes circuit 3| to pick up Y3 and to hold X3 and A3 energized, and opens circuit 22, releasing Y2. The office relay Y2 at its back contacts (1 completes a branch 58 of circuit 32 to pick up relay SRI, and also completes a circuit 59 to pickup relay Pl. Relay Y2 at one of the two stations only, at which P6 is energized, completes a circuit I58 similar to circuit 58 to pick up relay P! at that station, while at the other station at which P6 is energized relay Z picks up; Relay SRI picks up and completes its stick circuit 6I from terminal B, back contact d of relay A-O, front contact a and winding of relay SRI to terminal C. Relays P! at the ofiice and selected station upon picking up complete their stick circuits 62, similar to circuit II]. This completes the station selection and further progression takes place at the office andv at the selected station only, because relay Z is picked up at all other stations.

Relays Y2 atcontacts 0 open the stick circuits 54, releasing the energized relays P6.

In the case of codes in which the sixth step is long, relay SR2 is picked up over a branch Seventh stepLong When each relay L2 picks up, circuit 36 closes and 3I opens so that relays X2 and A2 pick up, Y3 is held energized and X3 and A3 become deenergized. The character of this step is determined by the position of the switch lever SW, and

if this lever is normal, as shown, a circuit 65' is closed to pick up relay OT when relay X3 releases,

which extends from terminal 13', contacts d of relays SRI and SI, contacts g of relays PI l, PI6, P9, and P8, contact e of relay P1, left-hand contact b of lever SW, and thence over the same path as circuit 31 through relay T to terminal C.

However, it will be remembered that the codebeing described was initiated by reversing lever SW, and therefore circuit 65 is not effective and.

relay OT remains deenergized. Consequently, relay A3 releases, opening circuit 36 to deen'ergize relay A2, and closing circuit I4 to pick up relay B2. Relay A2 then'releases, opening circuit I4 to deenergize relay B2 and closing circuit 39 to pick up relay C2, and finally, relay B2 releases opening circuit 39 to deenergize relay C2 and closing circuit 40 to pick up relay D2. When theoffice relay B2 releases, it completes, at its back contact g, a circuit 66 which extends from terminal B to contact e of relay P1 over the same path as circuit to lever SW, thence over the right-hand contact 0 of lever W and over the same path as circuit 38 through relay OT to terminal C, so that relay OT picks up to open line 5.

When each line relay L2 releases, relay C2 or D2 will be in its energized position so that circuit 43 or 44 will close and circuit 39 or 46 will open, picking up relay Y2 and holding relays X2 and C2 or D2 energized, and releasing relay Y3. Relays Y3 at the ofiice and selected station at their back contacts (1 complete branches 61 of circuit I6 to pickup the corresponding relays P8, and

relays P8 complete their stick circuits 68. Relays Eighth stepShort When each line relay L2 picks up, a circuit 69 or 10, which is similar to circuit 22 but includes contact 0 of relay C2 or D2, becomes closed, in.

case the preceding step is long, or circuit 22 closes,

in case the preceding step is short, to pick up X3 and A3 and to hold Y2 energized. Circuit 43 or 44 opens to deenergize relays X2 and C2 or D2 if the preceding step is long, or circuit I5 opens, to deenergiz-e relays X2 and A2 in case the preceding step is short.

Since in the code described the preceding step was long, lever SW being reversed, it followsthat' when X3 picks up; a circuit I H- iscl'osed momen' tarily from terminal B, contact I; of relay CR at the selected station, contact c of relay X3, contact e of relay C2 or D2, contact of relay P8, the right-hand winding of the polar-stick switch control relay WS to terminal C. If the preceding step Were short (lever SW normal) a similar circuit I12 would be closed at this time over contact e of relay A2, contact at of relay P3 through the left-hand winding of relay WS. Relay WS will be operated to the right or left over circuit III or H2 in acordance with the position of lever SW, and remains in its last-operated position until it is again energized.

The character of the eighth step is determined by the position of the signal lever LG, and with this lever in its normal or stop position, as shown, the eighth step is short because a circuit I3 is completed from terminal B at front contact d of relay SRI, over contact d of relay SI, contacts g of relays PI I, PIE! and P9, contact e of relay P3, contact b of lever LG and thence over the same path as circuit 2'! over contact f of relay A3 through relay OT to terminal C. Relay OT picks up over circuit I3 to open line 5 when the oiiice relay X2 releases and closes its contact (2.

If lever LG had been in its left-hand or clear position circuit I3 would be ineffective, so that relay OT would remain deenergized and circuit 69, III or 22 would open and circuit 23 close to pick up relay B3 in series with relays X3 and Y2 0 upon the release of relay C2, D2 or A2. Relay A3 upon releasing due to the opening of circuit 22 would close circuit 24. and open circuit 23 to pick up relay C3 and deenergize relay B3, and relay B3 upon'releasing would complete a branch 14 of circuit 26 over the left-hand contact I) of lever LG and contact f of relay C2 to pick up relay OT.

In either case, when relay OT picks up to open line 5 each relay L2 releases and closes circuit 3 I, 28 or 29 to pick up relay Y3 and to hold relay X3 energized in series with relay A3, C3 or D3, and opens circuit 69, I0 or 22 to release relay Y2. Relays Y2, upon releasing, complete circuits I5 to pick up relays P9 and open circuits 68 to release relays P8, and relays P9 complete their stick circuits I6 at the office and selected station. The office relay P3 upon picking up opens circuit 13 or I4 so that relay OT releases to close line 5.

Ninth stepSh0rt When each line relay L2 picks up circuit 35, 33 or 35 closes to pick up relays X2 and A2 and to hold relay Y3 energized, and circuit 3i, 28 or 23 opens to deenergize relays X3 and A3, C3 or D3.

Since the preceding step was short (lever LG normal) relay A3 is now picked up but deenergized and when relay X2 picks up a circuit IT! is closed momentarily at the selected station from terminal B, contact I) of relay CR, contact 0 of relay X2, contact e of relay A3, contact d of relay PS, the left-hand winding of relay LHS to terminal C. If the preceding step were long (lever LG at the left) relay C3 or D3 would be picked up and a similar circuit I13 would be closed over contact e of relay C3 and D3, contact 0 of relay P9, the right-hand winding of relay LHS to terminal C. In either case relay LHS will be energized momentarily in a direction to operate it to a position to correspond with that of lever LG.

The ninth step is short when signal lever RG is in its normal position, as shown, and is long when lever RG occupies its right-hand position, and its length is determined by circuits I9 and 80 for relay OT similar to circuits 65 and 66 already described. When relay X3 releases relay OT picks up over circuit I9 or 89 and opens line 5. Each line relay L2 releases to close circuit I5, 43 or 44 to pick up relay Y2 and to hold relay X2 energized in series with relay A2, C2 or D2 and to open circuit 33, 34 or 35 to release relay Y3.

Relays Y3, upon releasing, complete circuits 3| to pick up the relays PIE] and open circuits 16 to release relays P9, and relays PIIJ complete their stick circuits 82 at the ofiice and selected station. The ofiice relay PIII upon picking up opens circuit I9 or 88 so that relay OT releases to close line 5.

Tenth stepShort When each line relay L2 picks up, circuit 22, 69 or I0 closes to pick up relays X3 and A3 and to hold relay Y2 energized, and circuit I5, 43 or 44 opens to deenergize relays X2 and A2, C2 or D2.

Relay RHS is now operated to the left or right over a circuit I83 or I84 in accordance with the position of lever RG, the circuits being similar to circuits Ill and I72 for relay WS already described.

The length of the tenth step is determined in accordance with the position of the call-on signal lever CO by means of circuits 85 and 83 for relay OT which are similar to circuits I3 and I4 controlled by lever LG already described. When relay OT picks up over circuit 85 or 86 each line relay L2 releases and closes circuit 3|, 28 or 29 to pick up relay Y3 and to hold relay X3 energized in series with relay A3, C3 or D3, and opens circuit 22, 39 or Ill to release relay Y2. Relays Y2 upon releasing complete circuits 8'. to pick up relays PI I and open circuit 82 to release relays PH), and relays PII complete their stick circuits 88. The office relay PII upon picking up opens circuit 85 or 86 so that relay OT releases to close line 5.

Eleventh stepShort When each line relay L2 picks up circuit 36, 34 or 35 closes to pick up relays X2 and A2 and to hold Y3 energized, and circuit 3|, 28 or 29 opens to deenergize X3 and A3, C3 or D3.

Relay CHS is now operated to the left or right over a circuit I 89 or I98 in accordance with the position of lever CO, these circuits being similar to those for relay LHS already described. The eleventh step is short in all control codes, and relay OT is picked up over a branch 9| of circuit 37 over contact 6 of relay PI I, which closes when relay X3 releases. When relay OT picks up over circuit 9| and opens line 5 each line relay L2 releases to close circuit I5 to pick up relay Y2 and to hold relays X2 and A2 energized and to open circuit 36, 34 or 35 to release relay Y3.

Relays Y3 upon releasing complete circuits 92 to pick up relays PI2 and open circuits 88 to release relays PI I, and relays PI2 complete their stick circuits 93.

The oflice relay Y3 now completes at its back contact at a circuit 94 for relay PC comprising a branch of circuit I6 extending from terminal B over contact 1 of relay PI I, the normal contact of the recall key RC, contact f of relay OM, the left-hand winding of relay PC to terminal C. Relay PC therefore operates its contacts a and b to the left, so that when relay OT releases current of normal polarity will be delivered toline 5.

When the ofiice relay PI2 picks up it opens the stick circuit 3 for relay SPI at its contact it, since contact h of relay SI is now open, and relay SPI releases. At contact g, the ofiice relay PI2 opens circuit 9| to release relay OT to close line 5.

Twelfth step Since the line circuit now becomes energized by current of normal polarity relays LI at the oflice and at all stations pick up, and each at contacts a closes a circuit 95 from terminal B over contact b of relay Y0, the upper winding of relay X0, relay A to terminal 0, so that relays X0 and A0 pick up. At the same time circuit I is opened at contact at of relay LI so that relays Y2, X2 and A2 release. Relays Y2 open circuits 93 releasing relays PI2. Relays PI3 are not operated during a control code unless the recall key RC is operated, as hereinafter described.

When the office relay A0 picks up it opens circuit BI, releasing relay SRI.

When the oihce relay X0 picks up it opens the stick circuit I9 for relay OM at its contact b and relay OM releases. The office relay X0, at contact 0, closes a circuit 95 from terminal B over contact a of relay ST, relay OT to terminal C so that relay OT picks up and opens line 5 to terminate the line-closed portion of the twelfth step.

Relays LI therefore release, and each closes a circuit 91 to pick up relay Y0 and to hold relays X0 and A0 energized, which at the ofiice extends from terminal B, contact b of relay LI, upper winding of relay Y0, contact a and winding of relay X0, contact a and winding of relay A0 to terminal C. Circuits 97 at the field stations are similar, but each includes, in addition, a back contact ,1 of relay L2. The office relay Y0 at'contact c closes circuit I! to reenergize relay ST. When relay ST picks up its contact g opens circuit 95, releasing relay 0T to close line 5.

Restoration to normal All relays LI now pick up and remain steadily energized and each closes a circuit 98 from terminal B over its contact 0, upper winding of relay XI, contact a and lower winding of relay Y0, contact b of relay A0, relay Al to terminal 0, so that relays XI and AI pick up and Y0 is held energized. At the same time circuit 91 is opened and relays X0 and A0 are deenergized. At each station at which the look-out relay Z has been picked up, that relay now releases due to the opening of circuit I33 at back contact I) of relay XI. When each relay A0 releases it opens circuit 98 at its contact I) to deenergize relay AI and closes a circuit 99 at its contact h to pick up relay BI in series with relays XI and Y0. When each relay AI releases, it similarly opens circuit 99 and closes a circuit I to deenergize BI and to pick up relay CI in series with relays XI and Y0. When each relay BI releases, it opens circuit I00 and at its contact 71. completes the normally closed holding circuit 6 for relays XI, Y0 and CI. When the station relays CI pick up, each at its contact 71. opens circuit I2I releasing relay CR. All of the apparatus, with the exception of lever SW and relay WS, which have been reversed, has now been restored to its normal condition.

If a starting relay such as S2 has been released during the transmission of' the code just ell) described, the corresponding sending relay SP2 will pick up over circuit 2 when relay ST picks up during the line open period at the end of the twelfth step. Then when the line becomes steadily energized, relays A0, AI and BI release successively as described, circuit 4 becoming closed at contact 9 of relay BI to pick up relay OT and thereby initiate the new code, when relay BI releases. The two codes are thus separated by a long positive impulse following the short positive twelfth step of the first code.

The transmission of a typical indication code will now be described. As shown in Fig. 2B, the

will be assumed that the coding apparatus is in its normal condition, as shown, but that the track switch at station No. 1 has been operated to reverse as a result of the reversal of relay WS by the control code already described. When the movement of the track switch is completed, the switch indication relay KR becomes energized in the reverse direction, opening circuit IllI at its contact a. This initiates the code and it is to be understood that the station code call will be represented by one long and four short impulses, as in the control code to which the apparatus at station No. 1 is responsive, and that all the function elements of the code are short steps except the seventh step controlled by contact c of relay KR which is long to indicate that the track switch is reversed.

Relay S, at station No. 1, at its contact g completes a circuit I02 from terminal B, contact 0 of relay XI, Fig. 2A, contact or of relay M, contact g of relay S through the left-hand winding of the polar stick relay SP to terminal C. Relay SP operates its contacts to the left, closing a circuit I03 from terminal B over its contact I) and the contacts 9 of the P relays, contact 0 of relay Y0, relay ST, Fig. 2A, to terminal 0.

The station relay ST picks up and completes a circuit I04 which extends from terminal B over the same path as circuit H93 in Fig. 2B, but which is completed in Fig. 2A over contact 1 of relay CI, contact 9 of relay BI, contact d of relay XO, contact a of relay ST, relay T to terminal C. Relay T therefore picks up and at its contacts a and b opens the line circuit 5 deenergizing the plus line relays LI at the oifice and at all stations.

The release of the line relays LI has the same result as in the case of the control code already described; that is, circuit 6 is opened and I closed, picking up the relays Y3, holding relays XI and CI energized and releasing relay Y0; circuit 8 closes, reversing PC; and circuits 9 and I0 close picking up and sticking relays PI.

When the station relay PI picks up, it opens circuit I04 at its contact g, releasing relay T to close line 5. Relay Y0 upon releasing opens circuit I03 to release relay ST.

The character of the first step of the code determines the direction of transmission, being short in a control code and long in an indication code.

Since relay PC is now reversed, the closing of line 5 by relay T causes the minus line relays L2 to pick up, each closing circuit I2 and opening circuit I32. Each relay CI upon releasing opens circuit I2 and closes circuit I4, deenergizing re lay A2 and energizing relay B2 in series with relays X2 and Y3. Each relay A2, upon releasing, opens circuit I4 and closes circuit 39, deenergizing relay B2 and energizing relay C2 in series with relays X2 and Y3. The station relay B2, upon releasing, closes a circuit I I3 for relay T which extends over the same path as circuit I83 from terminal B to contact g of relay P2 and then extends over contact e of relay PI, contacts 1 of relay C2, contact g of relay B2, contacts d of relays X3 and XI, relay T to terminal C. Relay T therefore picks up over circuit I I3 to open line 5.

When line 5 opens, relays L2 release and close circuits 43 to pick up relays Y2 and to hold relays X2 and C2 energized, and open circuits 39 to release relays Y3. Each relay Y3 upon releasing, closes circuit I6 to pick up relay P2 and opens circuit It to release PI, and each relay P2 closes its stick circuit II. The relay'Y3'at the transmitting station closes a circuit H8 from terminal B at contact 11 of relay YO over the same path as for circuit M5 to contact c of relay PI, thence over that contact and contact 0 of relay SP, relay M to terminal C. Relay M upon picking up closes its stick circuit II9 which extends to terminal B over contact 9 of relay CI and contact 2; of relay XO.

Relay Y3, at the office, upon releasing, closes a branch 20 of circuit 45 over contact e of relay PI to pick up the indication register relay IR, which upon picking up completes its stick circuit 2I which extends to terminal B over its contact a and contact h of relay Ci. Relay IR remains energized until the code transmission is completed.

When relay P2 at the transmitting static-n picks up, it opens the energizing circuit 1 I 3 for relay T at its back contact g so that relay T releases to close the line circuit 5.

The operations on second to sixth steps, inclusive, of the indication code are identical with those effected during the corresponding steps of the control code already described, except that the transmission is governed by the station relay T, which is energized successively over branch circuits I26, I31, I45, I5I and IE6 similar, respectively, to the circuits 25, 3.7, 48, 5E and 56 for the office relay OT already described.

At each other field station, relay Z will be picked up on one or another of these steps, over circuit I32 as in the case of a control code, so that the relay progression continues beyond the fifth step at the ofiice and transmitting station only. On the sixth step, relay S picks up over a circuit I 56 similar to circuit 56 already described, and closes its stick circuit IOI, and at its contact 0 prepares circuits for controlling relay T on succeeding steps.

The indication code has six function steps, two more than the control code described. On the seventh and eighth steps, relay T is controlled, respectively, over the polar contact 0 and the neutral contact I) of the switch indication relay KR, and since it has been assumed that this relay is energized in the reverse direction, relay T will be energized over circuits I66 and I73, respectively, corresponding to the ofiice circuits 6% and I3 already described, to produce a long seventh step and a short eighth step, each of which is registered at the oifice on the next succeeding step by the momentary energization of a polar stick indication relay. Since the seventh step is long, it will be found that relays X3 and C2 01' D2 are in their energized positions at the beginning of the eighth step, and a circuit H is closed from the middle terminal 0 of the local battery, Fig. 13, through the winding of the switch indication relay IWK, contact 0 of relay P8, contact b of relay SRI, contact 0 of relay X3, contact 17 of relay IR, contact 6 of relay C2 or D2 to terminal 0, energizing relay IWK in the reverse direction to close its right-hand contact a. If the seventh step were short, relays X3 and A2 would be in their energized positions at the beginning of the eighth step, and a circuit I2 would be closed at the beginning of the eighth step which extends from terminal B, contact e of relay A2 and thence over the same path as for circuit II through relay IWK to the middle terminal O of the local battery, to cause relay IWK to move contact a to the left, as shown.

The eighth step being short, at the beginning of the ninth step, relays X2 and A3 are in their energized positions and a circuit I1 is closed from terminal B, contact e of relay A3, contacts 0 of relays IR, X2, SRI and P3, relay ILK to terminal 0 to operate relay ILK to the left. When the eighth step is long, a circuit 58 similar to 1! but including contact e of relay C2 or D2 closes at this time and relay ILK is operated to the right.

It is to be noted that when the movement of the track switch from normal to reverse is initiated, relay KR releases, transmitting a code to energize relay I WK in the normal direction and relay ILK in the reverse direction, and the normal switch indication lamp NWE is extinguished by the opening of contact a of relay ILK. When the switch completes its movement to reverse an indication code is transmitted to energize relay IWK in the reverse direction and relay ILK in the normal direction, as described, to light the reverse switch indication lamp RWE, as will. be apparent from the drawings.

In a similar manner, the signal repeating relays LGP and RGP and the track relays TR and AR control the character of the ninth, tenth,

eleventh and twelfth steps. When the signals indicate stop, LGP and RGP are both energized, the ninth and tenth steps are short, relays iLGK and IRGK are both operated to the left and lamp NGE is lighted. When signal LG or RG is clear, relay LGP or GRP is released and the corresponding code step is long so that ILGK and IRGK are operated to th right to light lamps LGE and RGE, as the case may be.

Similarly, the eleventh and twelfth steps are short or long depending upon whether the relays ITR and IAR, respectively, are energized or released, relays ITK and I i being operated to the right to light lamps ITE and IAE by long impulses on the 12th and 13th steps, respectively, to indicate the occupancy of the respective track sections.

At station No. 2, the jumper connection for relay S will be arranged to connect circuits I56 and I26, so that when an indication code is initiated at station No. 2, the sixth step will be long to effect the energization of relay SR2 over circuit 63, in place of relay SRI, and another set of indication relays K, not shown, but similar to those associated with the control panel for station No. 1, will be operated over circuits such as II and IT, as will be apparent from the drawings.

The stepping operations on the seventh to eleventh steps, inclusive, of an indication code are the same as for the control code already do- All relays LI now pick up and remain steadily scribed, but since the indication code includes two additional steps the succeeding operations are different. Circuit 94 is open at contact 1 of relay OM, and consequently it does not become closed to restore relay PC to normal during the line-open period of the 11th step. It follows that in an indication code, the 12th step is of negative polarity, and relays L2 pick up when relay T releases and closes line 5 at the beginning of the twelfth step, as on preceding even numbered steps, closing'circuits 22 and opening circuits I5 to pick up relays X3 and A3, to hold relay Y2 energized, and to deenergize relays X2 and A2.

Relay ITK is energized momentarily on this step, as already pointed out, and when relay X2 releases, relay T is energized selectively to determine the length of the step over a circuit I05 or I06 including contact e of relay PI2, When relay T picks up, relays L2 release and each closes circuit 2|, 28 or 29 to pick up relay Y3 and to hold relay X3 energized in series with relay A3, C3 or D3, and opens circuit 22, 69 or I to release relay Y2. Relays Y2 upon releasing complete circuits I0I to pick up relays PI3, and open circuits 93 to release relays PI2, and relays PI3 complete their stick circuits I 08. The station relay PI3 upon picking up opens circuit I or I06 so that relay T releases to close line 5.

At the beginning of the thirteenth step, line relays L2 pick up, closing circuits 36 and opening circuits 3I to pick up relays X2 and. A2 and hold Y3 energized, and to deenergize X3 and A3.

Relay IAK is energized momentarily on this step, as already described, and when relay X3 releases, relay T is energized over a circuit I09 including front contact e of the station relay P I 3. The thirteenth step therefore is a short impulse, and relays L2 release, closing circuits I5 to pick up relay Y2 and to hold X2 and A2 energized, and opening circuits 36 to release Y3.

The ofiice relay Y2 upon picking up closes a branch I94 of circuit H from terminal B at contact d of relay YO over contact b of the office relay PI3, through the left-hand winding of relay PC to terminal C. Relay PC therefore operates its contacts a and b to the left during the line-open period of the thirteenth step.

When the station relay Y3 releases, it opens circuit I08 to deenergize relay PI3 and at the same time closes a branch IIO of circuit I6 from terminal B over contact I) of relay PI3 through the right-hand winding of relay SP, energizing relay SP momentarily to restore it to its reverse position, as shown. Relay SP at contact a opens circuit I09 to deenergize relay T.

When relay T releases, line' 5 becomes energized. by current of normal polarity to begin the fourteenth step, and relays LI at the ofiice and all stations pick up, closing circuits 95 to pick up relays X0 and A0, and opening circuit I5 to release Y2, X2 and A2, as already described in connection with the twelfth step of th control code.

The office relay AO upon picking up opens circuit 6|, releasing relay SRI. The station relay XO upon picking up opens circuit II9, releasing relay M. At the same time the oilice relay XO closes circuit 96 to pick up relay OT to open line 5.

Relays LI release, and, as already described, close circuits 91 to pick up relay Y0 and to hold X0 and A0 energized. The oflice relay YO closes circuit II, picking up the office relay ST, which opens circuit 96 releasing OT to close line 5.

energized and close circuits 98 and open circuits 91 to pick up relays XI and Al, to hold YO energized and to release relays X0 and A0. Relays XI open circuits I33 to release relays Z at the stations at which these relays have been energized, and as the end of a control code, circuits 99, I00 and 6 close to energize relays BI and CI successively and to completethe stick circuit for energizing relay CI in series with relays XI and Y0, as shown. When the ofiice relay CI picks up circuit 2I opens to release relay IR. All of the apparatus with the exception of lever SW and relays KR and IWK which are reversed, is now in its normal condition, as shown.

If a starting relay such as relay S has been released at any station during the transmission of the code just described, the corresponding relay SP will be reversed by the closing of circuit I02 when relay XI picks up upon the restoration of the line to normal. Relays AO, AI and BI then release successively, circuit I04 closing at back contact g of relay BI to initiate the new code when relay BI releases. The two codes are thus separated by a long positive impulse following the short positive 14th step of the first code.

Our apparatus includes a novel recall feature by means of which the operator may cause an indication code to be initiated without causing a change in the condition of any of the station devices. This is accomplished by reversing the recall key RC, Fig. 1B, and by then opening circuit I by momentarily reversing one of the control levers. This results in the transmission of a control code which difiers from that hereinbefore described in that it includes one additional step. Circuit 94 is not closed to restore relay PC to normal on the 11th step, and consequently, line 5 is energized by current of reverse polarity on the 12th step, as in the case of an indication code. The 12th step is short, because relay OT is energized over the branch I96 of circuit 21 which extends to terminal B over contact e of relay PI2 and contact g of relay PI3. Relay PC is restored to normal when relay Y2 releases on the 12th step by energization over a circuit 94a which extends from terminal B at contact d of relay YO over the same path as circuit 59 to contact 1 of relay PI2, thence over that contact and the reverse contact of the recall key RC, contact 1 of relay OM through the lefthand winding of relay PC to terminal C. Relay PI3 picks up over circuit I01 and opens circuit I96, deenergizing relay OT, and when relay OT closes line 5 to begin the 13th step, line relays LI will pick up, the remaining operations involved in restoring the apparatus to normal being 7 similar to those previously described. Th recall code, however, will produce a different result at the selected station. Since the 11th step of the code is short,. relay A2 will be in its energized position at the beginning of the 12th step and since the 12th step is negative relay X3 will pick up to close a circuit I02a momentarily from terminal B at contact b of relay CR over the same path as circuit I12, front contact d of relay PI2, the left-hand Winding of relay SP to terminal C. Consequently, relay SP will be operated to the left by the control code and will connect terminal B, to circuit I03, so that circuit I04 will become closed when relay BI releases following the restoration to normal at the end of the code, thereby initiating the transmission of an indication code, the two codes being separated by a long positive impulse as in the cases previously described.

Our apparatus is so arranged that after a code has been initiated by any transmitter it can not be interfered with by the operation of other transmitters, and also so that if two or more codes are initiated simultaneously, no interference will occur, but the codes will be transmitted one at a time in a predetermined order of code superiority.

No station relay SP can be operated to the left by the release of the associated relay S during transmission because circuit IE2 i opened by relay XI which releases when the line circuit is opened. at the beginning of a. code. Similarly, no office relay such as SPI can pick up during transmission because its pick-up circuit 2 is similarly controlled by the office relay ST. It may happen, however, that two or more relays such as SP! and SP are operated at the same time.

Since all circuits for the station transmitter relay T, except the initiating circuit I04 and circuit II3 for producing a long first step, include front contacts of relay M, relay M must pick up in order to permit a station to continue transmission beyond the first step. The pick up circuit H8 for relay M is a branch of circuit I45 and closes only when the first step of the code is a long impulse. If the oiiice and one or more stations start simultaneously, the station apparatus will be unable to prevent the oflice relay OT from opening line 5 to produce a short first step, consequently, none of the station relays M can pick up; relay OT will remain in control of the line, and relay OM at the office will pick up over'circuit I8, which closes only when the first step of the code is a short impulse, and the office transmitter will remain in operation.

Relays CR at the stations will pick up in response to the short first impulse to condition the stations to register the control code while the office relay IR will remain deenergized.

If two or more stations start simultaneously, their transmitting relays T will be held in step by the line relays only as long as the code steps are of identical character. As soon, however, as a station attempts to transmit a long impulse while another station is transmitting a short impulse, its operation will be discontinued. Assume that station No. I starts to transmit the indication code hereinbefore described, and that at the same time another station starts a code having a short second step. At station No. I, the line relay L2 will release at the end of the line-closed portion of the second step while relay A3 is picked up, that is, before relay C3 has picked up to prepare circuit I30 for relay P3, consequently, relay Z will pick up over circuit I32, and relay P2 will release without energizing relay P3, circuit I3! will remain open, and consequently relay T at station No. I will remain deenergized and the code being transmitted by the other station will continue without interference. The operation of the timing relays at station No. I is discontinued due to the opening of contacts b and c of relay Z.

It will be apparent that a similar result may occur on any station selecting step of the code, and that the selection as to which station will retain control of the line is on the basis of code superiority, the transmission of a short impulse on any step taking precedence over a long impulse.

Since the office control levers may be operated individually or in any combination at any time, it may happen that a plurality of code sending relays such as SP! and SP2 are picked up at the same time and provide a multiple energization of circuit 4 to initiate different control codes. On any station selecting step, it is obvious that the circuit such as 21 or 56 for picking up relay OT to produce a short code element will be closed before the corresponding circuit 26 or 51 for producing a long element can be closed and will effect the energization of the proper relay P to render the latter circuit ineffective. Consequently, but one relay, SP2 for example, will remain in control of relay OT, and no interference between the stored codes will occur. Each code sending relay SP at the oilice will be released at the end of the last negative step of the code provided the associated starting relay is reenergized during the tranmission of the 6th step of the corresponding code, and the stored codes will be transmitted one at a time in order.

As explained more fully in the Snavely, Miller and Jackel Patent No. 2,183,155 hereinbefore referred to, the station apparatus may be provided with a plurality of series of relays P such as are provided for the ofiice apparatus described herein, when there are a plurality of storage units, or groups of controlled devices at a station to be controlled and indicated by the station coding apparatus. When the station apparatus is so arranged, there will be a plurality of relays SP at a station, one for each storage unit, and these relays SP may have their contacts b closed at the same time to initiate different indication codes. It is evident that, as in the case of the ofiice apparatus, the station apparatus may be so arranged that but one relay SP will remain in control of relay T and no interference will occur.

If two or more control levers of a group such as levers SW and LG associated with station No. I are operated, it is evident that the code will contain the proper function steps corresponding to the new positions of all the levers that have been operated provided these operations are completed in time to permit the starting relay such as SI to pick up over circuit 56, which circuit closes prior to the transmission of the first function step of the code. A lever movement occurring during the transmission of the function steps will open circuits I and 2 at the lever contact a and cause relay SI to release and open the circuits for relay OT. This causes the apparatus to subsequently transmit a new code, thereby insuring that the function steps of a completed control code correspond to the final positions of the levers.

Since the station circuits are similarly arranged, it will be evident that similar considerations apply, in the event one or more of the indication controlling devices change their positions during the transmission of an indication code from the corresponding station.

In accordance with another feature of our invention, our apparatus is so arranged that stored codes are usually transmitted in the order in which they are stored, and only in accordance with the relative code superiority when the codes are stored at the same time, or prior to the initiation of a series of codes. When a plurality of control codes are stored while the line is in use, the ofiice will transmit all the stored control codes in the order of code superiority when the line becomes free, before it transmits any control codes that become stored while these stored codes are being transmitted. Similarly, when the stations obtain control of the line, one indication code will be transmitted from each station storage unit which has at that time a code stored for transmission, before any station storage unit can transmit a second code, and also before the office can transmit a code which becomes stored while the stored indication codes are being transmitted.

To explain this feature of our invention it will first be assumed that levers for controlling devices at station No. I and at some inferior station No. 3 are operated, either at the same time or while indication codes are being received.

In either case, pick-up circuits 2 for the two relays SPI and SP3 will be closed so that both willpick up and will jointly energize circuit 4 to initiate a control code when the line becomes available, which by reason of code superiority mitted will be the one for station No. I, but there;

are now two or more control codes stored for subsequent transmission. Because the code for the inferior station No. 3 was stored first, it will be transmitted first, as will now be explained.

The first control code will progress as hereinbefore described up to the final, or 12th step, at which time the line relays LI pick up to open circuit I5 and close circuit 95 to energize relays X0 and A0 and release relays X2, Y2 and A2,

as already described. The ofiice relay X0 upon picking up opens the normal stick circuit I9 for relay 0M, at its contact 11, but relay OM does not release If there are other control codes stored for transmission, but remains energized over an auxiliary stick circuit 60 which is closed at this time by relay A0, comprising a branch of circuit 4 which extends from terminal B at front contact I) of any relay SP which is already picked up, such as relay SP3 over back contacts g of relay SR3 and back contacts of the corresponding series of relays P6 to Pl, contact 1 of relay A0, contact g of relay CI, contact a, and winding of relay OM to terminal 0.

It may be noted that relay SP3 now controls circuit 6|] because relay SPI was released when relay PI2 picked up. at the end of the 11th step, and relay SP2 has not been picked up.

As in the case of the control code previously described, the oilice relay X0 at its contact 0 closes circuit 96, causing relay CT to open line 5, to terminate the line-closed position of the twelfth step, thereby releasing relays LI, whereupon circuits 91 close to pick up relay Y0 and to hold realys X0 and A0 energized, the oflice relay Y0 closing circuit II to pick up relay ST. Relay ST connects terminal B to circuit 2, but this circuit is now held open at back contact 9 1 of relay OM. It follows that although relay S2 has been released, relay SP2 does not pick up at this time. Relay ST opens circuit 96, releasing relay OT and closing line 5.

In the cases previously described, this initiated the return to normal at the end of the code, or the beginning of the long positive impulse interposed between successive codes, but

in the present case,it represents the beginning of the first step of the second code of the series, which is a short positive step. Since relay PC is still normal, relays LI pick up, closing circuits 98 and opening circuits 91 so that relays XI and AI pick up, relays Y0 and ST are held energized, and X0 and A0 are deenergized.

The office relay A0 now opens the auxiliary stick circuit 60 and at the same time relay X0 reestablishes the normal stick circuit I9 for relay 0M and also closes a circuit 4a for relay 0T from terminal B at front contact b of relay SP3 over the same path as for circuit 60 just traced to contact 9 of relay PI, thence over contact 17 of relay 0M, contact I of relay AI, contact d of relay X0, contact a of relay ST, relay CT, to terminal C. Relay 0T, upon becoming energized over circuit 4a, opens line 5, releasing relays LI. Each relay LI upon releasing closes a circuit II2 from terminal B, contact d of relay LI, contact b of relay L2, relay Y2, contact I) of relay X2, contact e of relay AI, contact a and. winding of relay XI, contact a and winding of relay Al to terminal C. Relays Y2 pick up and relays XI and AI are held energized over circuits H2, and circuits 98 are opened, releasing relays Y0. Since relay XI has been picked up, the release of the oflice relay LI closes circuit 8 to position relay PC to the right at this time. Relays PI, it will be noted, have not been operated,

When relays YO release, each relay P2 picks up over circuit II 4 extending from terminal B, contact at of relay YO, contact 0 of relay Y2, contact d. of relay AI, relay P2, to terminal C, and each relay P2 then closes its stick circuit I1. The office relay P2 at contact 9 opens circuit 4a., releasing OT and thereby closing line 5. Since the relays CI have not been operated, the control register relays OR at each station remain energized.

This completes the first step of the second control code of the series, which, it will be seen, is a short positive step as distinguished from the short negative first step of the first control code of a series as hereinbefore described. The apparatus is now in the same condition as at the corresponding point of the control code first described. The apparatus continues to operate as hereinbefore described until the code for the inferior station No. 3 is completed. If other code sending relays in addition to relay SR3 were picked up when the series of codes was initiated, branches of circuit Bil will be completed to terminal B over contact b of such relays at the end of this code, and relay GM will not release until the corresponding codes have been transmitted. Relay GM will release at the end of the last of such codes, closing its contact 9 to prepare circuit 2 to pick up relay SP2, and any other relay SP for which the corresponding relay S is released, but will open circuit 4a at its contact I) so that the first code will be followed by a long positive impulse, terminated when relay 0T picks up over circuit 4 following the release of relay BI, as already explained in the description of the restoration of the apparatus to normal at the end of a code. Since relay XI picks up at the beginning of this long impulse, circuit 8 closes to reverse relay PC during the succeeding lineopen period, so that the next impulse, comprising the first step of the code for the superior station No. 2, will be of negative polarity.

The apparatus is now in the same condition as at the corresponding point of the control code first described, and will therefore continue to operate until the oflice panels for each of the stations No. 2, etc. transmit their codes in order. It will be seen that our apparatus functions as described because we have provided two sets of relays for storing the codes in two groups, one of which has priority over the other.

As already explained, the apparatus at a field station may also be arranged to have a plurality of storage units each comprising a relay S and a relay SP, as illustrated by the office apparatus of Fig. 1B, and when so arrangedthese relays will also function in the manner described to give priority to codes stored prior to the beginning of a series. This is also true when the codes are stored in storage units at different stations.

To make this clear, I will assume that the apparatus is arranged to have but one storage unit per station, as shown in Fig. 2B, and that devices at station No. I and at some inferior station No. 3 change positions at the same time, or while the line is not available, so that relays SP at the two stations are operated to the left over circuits I62 at the same time, to jointly initiate an indication code when the line becomes available by the simultaneous operation of their relays T, and that after the code transmission has started a device at the superior station No. 2 changes its position.

The relays T at stations Nos. I and 3 will be held in synchronism by the line relays L2 only as long as the code elements are alike. It will be assumed that the first, second and third steps of the code for station No. 3 are long, while in the code. for station No. I, as already described, the first and second steps are long and the third step is short. Consequently, relays M at both stations will pick up over circuit IIii on the long first step, and relays P3 will pick up at both stations over circuit I30 on the long second step. Relay T at station No. I will be energized over circuit I31 to produce a short third step. Consequently, relay PA will pick up at station No. I over circuit I45, while at station No. 3 the jumper connections in the circuits over contacts band c of relay P3 are interchanged so that relay Z will pick up, relays P2 releasing at both stations. Further progression at station No. 3 is stopped, as already explained, and although relay M at that station remains energized over its stick circuit I I9, the energizing circuits for relay T which it controls are not closed because no relay P is energized. The transmission by station No. I will continue as hereinbefore described up to the final, or 14th step, when the plus line relays LI pick up. At station No. I, which transmitted the code, relay M is released by the opening of circuit I I Q on this step, while at the inferior station No. 3, having a code stored for transmission, relay M is held energized over an auxiliary stick circuit I63 extending to terminal B over contact 02 of relay Z, which relay is now energized over its stick circuit 33. Relays LI are released on 7 this step by the energization of relay OT over circuit 96, as on the final step of a control code, and the code delivered by station No. I is completed when line is closed as the result of opening circuit 96.

This, as already described, results in again picking up relays LI, XI and Al to begin the return to normal when there are no codes stored for transmission but in the present case, although circuit I33 is opened at this time, releasing relay Z to open the auxiliary stick circuit I60 for the energized relav M at station No. 3. the normal stick circuit I it for that relay is reestablished by the release of relay X0 before circuit I opens. Consequently, relay M at station N0. 3 remains energized and as soon as relay AI pick up a branch tibia of circuit I EM is closed. Circuit I340, includes contact I) of relay M and corresponds to the office circuit 4a already described, so that relay T picks up at station No. 3 to open line 5. This constitutes the first step of the second indication code, which like the corresponding step of the second control code of a series is a short positive step as distinguished from the long negative first step of the first indication code of a series, and this step follows immediately after the last step of the preceding code.

At the office, relays Y0 and ST pick up, as already described, on the line-open period of the last step, and since relay OM has not been energized, circuit 2 becomes closed to pick up any relays SP for which the corresponding office relays S have been released as the result of lever movement occurring during the code just described.

Relays P2 pick up during the line-open portion of the first positive step of the second code over circuits IM and since the ofiice relays PI and CI are not operated, circuits 4, I3 and I8 are held open and the ofiice relays OT and OM do not pick up even though there are codes stored at the office, and circuit 2| remains closed so that the indication register relay IR remains energized.

When the station relays XI pick up during the line-closed portion of the first positive step, circuit I92 becomes closed at each station at which relay M is deenerg'ized, that is, at each station except station No. 3, to actuate relays SP if the relays S at such stations are released, but since the station relays PI and CI are not operated, circuits I64, H2 and IIS are held open and relays T and M at such stations do not pick up even though the stations have codes stored for transmission. Since relay M at station No. I releases before relay SP is actuated in response to a change in the position of a device at such station occurring during the transmission of the code by that station, it follows that station No. I will transmit but one code, and at the end of that code the inferior station No. 3 will assume control of the line even though the code sending relays at superior stations become actuated after the initiation of the code for station No. I.

The apparatus is now ready to begin the second step of the second indication code of the series, and is in the same condition a at the corresponding point of the indication code first described, and therefore continues to operate as described until station No. 3 completes its code. If no other relays M have been energized, the apparatus will restore to normal at the end of this code. After the transmission of a long positive impulse following the last impulse of the code from station No. 3, relays CI will pick up to close circuit I M at each station at which relay SP has been operated to initiate the transmission of a new series of indication codes.

It will be seen therefore, that any two groups of codes are separated by a long positive impulse, while any two codes of a group are separated only by a brief line-open period similar to the interval between any two steps of a code. Furthermore, the first step of each except the first code of a group is a short positive step, while the first step of the first code of a group is a long or short negative step, depending upon the direction of transmission. It will also be apparent that the direction of transmission is established by the first code of the group, and that all the stored codes for that direction will be transmitted before any codes for the opposite directions are transmitted.

It will be seen that under conditions of heavy traflic, codes will be transmitted from each office panel or station in turn until all the stored codes are transmitted and that new code storages established subsequently cannot delay the transmission of those codes previously stored, even though the new codes have superior code calls. In the absence of this feature, it is apparent that the transmission of certain code messages might be delayed to an extent greater than could be well tolerated.

Another result of this feature of our invention is that communication with the more superior stations is held up for longer time intervals than otherwise due to the more equal division of line time between the stations. Several successive changes in the positions of the levers for controlling the devices at such stations or in the positions of the indicating relays at such stations may be stored for transmission in a single code while otherwise each would require a separate code, so that the total number of codes is decreased and the traffic capacity of the system correspondingly increased.

Another feature of our invention resides in the arrangement of the apparatus so as to minimize the effect of a failure of any relay circuit upon the system as a whole. that on the third step of an indication code, the station relay T is energized over circuit I31 and is holding line 5 open as already described, but relay P4 fails to pick up to break circuit I31.

Relay T will not remain energized to prevent further use of the line because relay Y3 will release due to the opening of the circuit through its lower winding when relay L2 releases, and P3 will release due to the opening of circuit 33 by relay Y3. to release relay T, closing line 5, which will now remain closed with the L2 relays picked up. Each relay L2 closes circuit 22 and opens circuit I5, energizing relay A3 in series with relays X3 and Y2 and deenergizing relays X2 and A2. Relay A2 upon releasing, closes circuit 23 and opens circuit 22, energizing relay B3 in series with relays X3 and Y2 and deenergizing relay A3. Relay A3 then releases, closing circuit 24 and opening circuit 23, energizing relay C3 in series with relays X3 and Y2 and deenergizing B3, and when relay B3 releases, circuit 25 closes and circuit 24 opens so that relay D3 picks up in series with relays X3 and Y2 and (His deenergized. Relay C3 upon releasing, deenergizes relay D3 but maintains relays X3 and Y2 energized over circuit II5 until relay D3 releases. It follows that relays A2, A3, B3, C3, D3 and Y2 release successively in that order and when the office relay Y2 releases, a circuit H6 is closed from terminal B over contacts b of relays XI, Y2 and Y3, the left-hand winding of relay PC to terminal C to restore relay PC to normal. This releases the relays L2 and energizes relays LI and the apparatus is then restored to normal in the same manner as when relays LI pick up at the end of a complete code. A similar result occurs if there is a failure on any other odd-numbered step of a code, while on the even-numbered steps, a similar reset is obtained by the successive re- Assume, for example,

Relay P3 will then open circuit I31 lease of relays A3, B2, C2, D2 and Y3. Since relay Z at the transmitting station has not been energized, relay M at that station will be released in response to the energization of relay X0 by relay LI. It follows that other stations having codes stored for transmission, at which relays M and Z are energized, will take precedence and will transmit their codes before the station which failed can again initiate a code. This arrangement permits a station to repeat, as is desirable, in the event a code is not completed, but in sucha manner as to not interfere with the use of the line by other stations.

If the office apparatus for any reason is unable to complete a code, a similar reset action will occur, and the operations will be repeated until a complete code is transmitted, or until they are stopped manually by cancelling the code storages by the operations of the knock-down key KD to release the energized relays such as SI and SPI.

If a failure occurs during a line-closed period, it Will also prevent further progression, and the apparatus will similarly reset to normal.

This is because the circuits are so arranged that a failure of any of the relay circuits to close as intended will merely stop operation, and will not cause a false selection. Thus for example, when relay L2 picks up at the beginning of the first step, relays X2 and A2 are picked up in series over a circuit I2, and if L2 remains energized, relays B2, C2 and D2 are picked up successively in series with relay X2, over circuits I4, 39 and 40. The failure of any of these circuits to close at the proper time will cause relay X2 to release and prevent the closing of circuit I5 when relay L2 releases, so that the progression is stopped. The selection as to whether an impulse is registered as short or long depends upon the release periods of the A and B timing relays provided by the associated rectifier units. If the circuit for the unit associated with relay A2 is open, relay A2 will release quickly when relay CI releases and open the circuit I2 before relay B2 picks up over circuit I4, so that neither relay A2 nor C2 will be energized when relay L2 releases.

It will be apparent from the drawings that insurance against improper operation such as is provided in the few instances just described is provided in each of those circuits disclosed herein, and that the apparatus is not able to hold the line open for an extended period to prevent the use of the line by other stations.

Since the various relay operations are checked on each step and the end of the code is marked by a positive impulse, the number of steps in a code may be varied as required without sacrifice in the reliability of the apparatus.

One manner by which a step may be added to a control code to provide an additional function has already been explained in connection with the recall feature of the apparatus. Obviously a control element for any function of which the use is relatively infrequent may be added in this manner, so that it will be included in the control codes only when required. In practice the codes for the different stations do not necessarily have the same number of steps, but each may have as many function steps as there are devices to be controlled or indicated, since in each code the transmission of negative impulses continues until relay PC is actuated over a circuit 94, 94a or I94, and these circuits may be arranged to include contacts I of different P'relays'as re- 

